I know, and I use and like Telegram. But the result of optional end-to-end encryption is that most people don't use it. The whole idea of WhatsApp and Signal is to encrypt everything end-to-end to defeat mass surveillance.

Honest question - do you consider only surveillance done by governments as mass surveillance or would you add "surveillance" done by Facebook (to better target ads) also into that classification? The reason I ask is because metadata from WhatsApp (whom you messaged, when, from where, etc.) is used by Facebook unless you opted out (or if it's been declared illegal in the jurisdiction you live).

Signal is the only one to trust for security, privacy and handling mass surveillance better than the other apps.

Whether it's done by a government or Facebook, mass surveillance is still mass surveillance. But at least, with WhatsApp and Signal, only the metadata are observable, but not the content of my messages. It's still an issue, but something I'm willing to accept in exchange for a communication tool I can use with my non-technical friends, family, co-workers, etc.